Strategies for small-footprint devices in structural health monitoring

结构健康监测(SHM)已被提出，以允许航空航天工业从使用无损检测(NDT)技术进行的基于计划的维护过渡到基于状态的维护。最有前途的方法是使用安装在金属或复合材料结构上的原位压电陶瓷(PZT)换能器来产生和接收传播并与缺陷相互作用的超声导波。尽管已经提出了一些SHM技术，尽管飞机维护成本可能会降低，飞机可用性也会增加，但民用航空航天行业尚未实施这一方法。该计划旨在通过开发小尺寸PZT换能器阵列(约1 cm2)在高频下进行损伤量化的策略，在仍需满足的要求上实现重大突破：损伤量化(分辨率低于1 mm)、更小的占地面积以及SHM技术的耐用性。损伤量化将来自高频下的较小波长，以及使用紧凑阵列的更好分辨率的产生和测量位置。这项研究计划将沿着三个不同的研究方向进行。1)在损伤定量中，导波传播模式的识别是关键。因此，高频模式选择换能器将被设计成在PZT和主体结构之间的界面处产生目标应力分布，该目标应力分布是通过系统地优化模式功率流获得的。将通过创新的3D配置利用剪切应力和正应力的组合，以克服由于换能器尺寸减小而在结构中产生的减少的波功率，这可能会降低对损坏的敏感性。2)由于高分辨率损伤成像需要从检测和定位过渡到量化，超分辨率工具将被集成到基于相关的损伤成像算法中，该算法已经在更大的阵列上得到验证。PZT的动态模型以及它们在阵列内的机械和电气相互作用将被整合到用于关联的分析原子中，以获得更高的分辨率。3)PZT阵列的3D微制造将结合使用激光微机械加工技术从PZT块材烧蚀获得高功率密度，将溶胶-凝胶沉积与光刻技术相结合以实现穿透厚度和多层特征，以及组装诸如惯性质量等组件。用三维激光多普勒测振仪测量的速度场和损伤成像将用于验证所制备的PZT阵列。小尺寸PZT阵列的战略将允许通过更高的分辨率来量化损害，这种系统预计将通过较少干扰和对环境不那么敏感来实现所需的耐用性。

Structural Health Monitoring (SHM) has been proposed to allow the aerospace industry transitioning from scheduled-based maintenance, conducted using Non-Destructive Testing (NDT) techniques, to condition-based maintenance. The most promising approach uses in situ piezoceramic (PZT) transducers mounted on metallic or composite structures to generate and receive ultrasonic guided waves propagating and interacting with defects. Although a number of SHM technologies have been proposed, and despite the potential reduction of aircraft maintenance costs and increased aircraft availability, the civil aerospace industry has not implemented the approach yet. This program intends to achieve a major breakthrough on the requirements still to be addressed: damage quantification (resolution below 1 mm), smaller footprint, and demonstrated durability of SHM technologies, by developing strategies for small-footprint arrays of PZT transducers (in the order of 1 cm2) in damage quantification at high frequency. Damage quantification will come from smaller wavelengths at high frequency, and better resolved generation and measurement locations with a compact array. This research program will be conducted along three distinct research thrusts. 1) The discrimination of the guided wave mode propagating is critical in damage quantification. Thus, high-frequency mode-selective transducers will be designed to generate target stress profile at the interface between the PZT and the host structure, obtained from systematic optimization of modal power flow. Combined shear and normal stresses will be exploited through innovative 3D configurations to overcome the reduced wave power generated in the structure because of the transducer size reduction, potentially leading to reduced sensitivity to damage. 2) As high resolution damage imaging is required to transition from detection and localization to quantification, super-resolution tools will be integrated into the correlation-based damage imaging algorithms already validated for larger arrays. The dynamic model of the PZTs, as well as their mechanical and electrical interactions within the array will be integrated in the analysis atoms used in the correlation for higher resolution. 3) 3D microfabrication of the PZT arrays will combine ablation from a bulk piece of PZT for high power density, using laser micro-machining techniques, sol-gel deposition with photolithography techniques for through-the-thickness and multi-layer features, and assembly of components such as inertial masses. Velocity field measured with a 3D Laser Doppler Vibrometer and damage imaging will be used to validate the fabricated PZT arrays. Strategies for small-footprint arrays of PZT will allow damage quantification through higher resolution and such systems are expected to achieve the required durability by being less intrusive and less sensitive to environment.